1. Field of the Invention
The present invention relates generally to a method and apparatus for improving the output and efficiency of a combined cycle power generation plant and in particular to an improved method and apparatus for producing power by circulating a primary heat transfer fluid in a combined cycle power plant using Liquefied Natural Gas (xe2x80x9cLNGxe2x80x9d) or Liquefied Petroleum Gas (xe2x80x9cLPGxe2x80x9d) as a gas turbine fuel, utilizing cold energy associated with the vaporization to chill inlet air to the gas turbine, thereby increasing the efficiency of the gas turbine. During low ambient temperature conditions, when chilling of the gas turbine inlet air is not required, the LNG/LPG cold energy is used to cool the steam turbine condenser cooling water (secondary heat transfer fluid) to increasing the steam turbine efficiency and output.
2. Description of the Related Art
Combined cycle power plants use both steam and gas turbines to generate power. These combined cycle gas/steam power plants generally have produced a higher energy conversion efficiency than gas or steam only plants. The combined cycle plant""s efficiencies from 50% to 60%. These higher combined cycle efficiencies result from synergistic utilization of the combination of the gas turbine(s) with the steam turbine(s). Typically, combined cycle power plants utilize heat from the gas turbine exhaust to boil water to generate steam. These typical combined cycle plants are referred to as heat recovery steam generator (HRSG). The steam generated is utilized to power a steam turbine in the combined cycle plant. The gas turbine and the steam turbine can be utilized to separately power independent generators, or in the alternative, the steam turbine can be combined with the gas turbine to jointly drive a single generator via a common drive shaft.
LNG has been been utilized in combined cycle power plants as a fuel for the gas turbines. The advent of larger and more reliable gas turbines for generator drivers has been a key factor for increasing utilization of LNG as a power generation fuel for such gas turbines. Gas turbines can generate high volumes of heated exhaust gases. These heated gases can then be utilized to boil water and generate steam in a HRSG. The steam generated from the heated gas turbine exhaust is then used to drive a steam turbine, which in turn drives another power generator.
Combined cycle generation plant manifest various different arrangements and configurations. The thermal efficiency of a combined cycle generation plant, however, can approach 60% as compared to the thermal efficiency range of only 38 to 41% for a conventional steam turbine only power generation plant without a combined steam and gas turbine.
Gas fuel supply, however, has been a problem for the combined cycle power generation plants. LNG/LPG gas liquefaction, transportation, unloading, storage, vaporization, and utilization for power generation and/or feeding the existing pipelines is a major undertaking entailing hundreds of millions of dollars in capital investments. Because of these higher capital costs, LNG has typically been economically viable only for largest pipelines and power generation projects.
One feasible scenario is the xe2x80x9cintegrated energyxe2x80x9d approach. The integrated energy approach entails developing a single integrated project including all the steps from generating natural gas fuel via LNG liquefaction all the way through burning the fuel for power generation. The integrated energy approach has proven to be superior to sequentially developing independent projects along the energy supply line. Thus, the integrated energy approach is emerging as the preferred method because of its significantly lower project development and installation costs.
Privatization of the energy and infrastructure sectors in many developing countries is another factor in the growing utilization of LNG for power generation in combined cycle power generation plants. Millions of dollars can be saved in project development and construction costs by integrating the design, procurement, and construction of LNG/LPG receiving terminals with a combined cycle power generation plant utilizing LNG/LPG as a fuel supply. Some of the factors contributing to these huge savings include the optimization of LNG/LPG vaporization cold energy capture and utilization; optimization of the LNG/LPG combined cycle plant facility layout based on safety and energy efficient design considerations; integration of fuel unloading piers with water intake and discharge structures; integration of site development plans; utilization of common facilities for fire fighting, cooling water, electrical systems, administration and warehouse facilities; use of common non-manual construction staff; and finally integration of the construction schedules.
Moreover, with the increased demand for cleaner fuels, LNG now plays an even greater role in power generation, especially in countries that have to import natural gas. Since a great deal of energy is required to liquefy natural gas, an efficient capture of LNG cold energy associated with LNG vaporization can significantly improve a combined cycle power plant project""s cost effectiveness. The cold can be used to chill and densify intake air to the gas turbines and to cool steam turbine condenser cooling water to increase their efficiencies. The combined cycle plants provide higher efficiency than conventional steam power plants, however, a significant amount of energy is wasted. Typically energy is wasted that is generated in the form of heat from the combined cycle plant steam turbine condensers, heat from air passing into the gas turbine and cold energy generated during LNG vaporization. Thus there is a need to capture this heat and cold energy which is a by-product of the combine cycle power generation plants using LNG/LPG.
There is also a need to utilize LNG cold energy generated during LNG vaporization for chilling the air supply to a gas turbines and to cool condenser water to increase the output and efficiency of a combined cycle power plant. Thus, there is a need for a method and apparatus for increasing the output and efficiency of a combined cycle power plant by efficiently capturing heat and cold energy generated during combined cycle power generation.
The present invention meets the above mentioned needs by providing a method and apparatus for improving the output and efficiency of a combined cycle power generation plant by capturing heat generated in the power generation process to assist in the vaporization of LNG or LPG. Heat is recycled by circulating a warm primary heat transfer fluid through a vaporization heat exchanger associated with LNG/LPG vaporization process. The primary heat transfer fluid provides the heat for LNG/LPG vaporization. The present invention provides a heat transfer fluid which circulates to chill and densify inlet air passing through a gas turbine air intake. Chilling the gas turbine inlet air densities the inlet air and makes the gas turbine more efficient. Cooling the steam condenser cooling water increases steam turbine output. By removing heat from the gas turbine inlet air and/or from steam condenser cooling water, the plant output and efficiency is increased in a combined cycle power plant.